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Galambos AR, Papp ZT, Boldizsár I, Zádor F, Köles L, Harsing LG, Al-Khrasani M. Glycine Transporter 1 Inhibitors: Predictions on Their Possible Mechanisms in the Development of Opioid Analgesic Tolerance. Biomedicines 2024; 12:421. [PMID: 38398023 PMCID: PMC10886540 DOI: 10.3390/biomedicines12020421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 02/06/2024] [Accepted: 02/07/2024] [Indexed: 02/25/2024] Open
Abstract
The development of opioid tolerance in patients on long-term opioid analgesic treatment is an unsolved matter in clinical practice thus far. Dose escalation is required to restore analgesic efficacy, but at the price of side effects. Intensive research is ongoing to elucidate the underlying mechanisms of opioid analgesic tolerance in the hope of maintaining opioid analgesic efficacy. N-Methyl-D-aspartate receptor (NMDAR) antagonists have shown promising effects regarding opioid analgesic tolerance; however, their use is limited by side effects (memory dysfunction). Nevertheless, the GluN2B receptor remains a future target for the discovery of drugs to restore opioid efficacy. Mechanistically, the long-term activation of µ-opioid receptors (MORs) initiates receptor phosphorylation, which triggers β-arrestin-MAPKs and NOS-GC-PKG pathway activation, which ultimately ends with GluN2B receptor overactivation and glutamate release. The presence of glutamate and glycine as co-agonists is a prerequisite for GluN2B receptor activation. The extrasynaptic localization of the GluN2B receptor means it is influenced by the glycine level, which is regulated by astrocytic glycine transporter 1 (GlyT1). Enhanced astrocytic glycine release by reverse transporter mechanisms as a consequence of high glutamate levels or unconventional MOR activation on astrocytes could further activate the GluN2B receptor. GlyT1 inhibitors might inhibit this condition, thereby reducing opioid tolerance.
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Affiliation(s)
- Anna Rita Galambos
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvá-rad tér 4, H-1445 Budapest, Hungary; (A.R.G.); (Z.T.P.); (I.B.); (F.Z.)
| | - Zsolt Tamás Papp
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvá-rad tér 4, H-1445 Budapest, Hungary; (A.R.G.); (Z.T.P.); (I.B.); (F.Z.)
| | - Imre Boldizsár
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvá-rad tér 4, H-1445 Budapest, Hungary; (A.R.G.); (Z.T.P.); (I.B.); (F.Z.)
| | - Ferenc Zádor
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvá-rad tér 4, H-1445 Budapest, Hungary; (A.R.G.); (Z.T.P.); (I.B.); (F.Z.)
| | - László Köles
- Department of Oral Biology, Semmelweis University, H-1089 Budapest, Hungary;
| | - Laszlo G. Harsing
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvá-rad tér 4, H-1445 Budapest, Hungary; (A.R.G.); (Z.T.P.); (I.B.); (F.Z.)
| | - Mahmoud Al-Khrasani
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvá-rad tér 4, H-1445 Budapest, Hungary; (A.R.G.); (Z.T.P.); (I.B.); (F.Z.)
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Xie RG, Xu GY, Wu SX, Luo C. Presynaptic glutamate receptors in nociception. Pharmacol Ther 2023; 251:108539. [PMID: 37783347 DOI: 10.1016/j.pharmthera.2023.108539] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 08/19/2023] [Accepted: 09/25/2023] [Indexed: 10/04/2023]
Abstract
Chronic pain is a frequent, distressing and poorly understood health problem. Plasticity of synaptic transmission in the nociceptive pathways after inflammation or injury is assumed to be an important cellular basis for chronic, pathological pain. Glutamate serves as the main excitatory neurotransmitter at key synapses in the somatosensory nociceptive pathways, in which it acts on both ionotropic and metabotropic glutamate receptors. Although conventionally postsynaptic, compelling anatomical and physiological evidence demonstrates the presence of presynaptic glutamate receptors in the nociceptive pathways. Presynaptic glutamate receptors play crucial roles in nociceptive synaptic transmission and plasticity. They modulate presynaptic neurotransmitter release and synaptic plasticity, which in turn regulates pain sensitization. In this review, we summarize the latest understanding of the expression of presynaptic glutamate receptors in the nociceptive pathways, and how they contribute to nociceptive information processing and pain hypersensitivity associated with inflammation / injury. We uncover the cellular and molecular mechanisms of presynaptic glutamate receptors in shaping synaptic transmission and plasticity to mediate pain chronicity, which may provide therapeutic approaches for treatment of chronic pain.
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Affiliation(s)
- Rou-Gang Xie
- Department of Neurobiology, Fourth Military Medical University, Xi'an 710032, China.
| | - Guang-Yin Xu
- Jiangsu Key Laboratory of Neuropsychiatric Diseases, Institute of Neuroscience, Soochow University, Suzhou 215123, China
| | - Sheng-Xi Wu
- Department of Neurobiology, Fourth Military Medical University, Xi'an 710032, China.
| | - Ceng Luo
- Department of Neurobiology, Fourth Military Medical University, Xi'an 710032, China.
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Persistent Activity of Metabotropic Glutamate Receptor 5 in the Periaqueductal Gray Constrains Emergence of Chronic Neuropathic Pain. Curr Biol 2020; 30:4631-4642.e6. [PMID: 32976802 DOI: 10.1016/j.cub.2020.09.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 07/15/2020] [Accepted: 09/03/2020] [Indexed: 12/13/2022]
Abstract
Pain sensation is powerfully modulated by signal processing in the brain, and pain becomes chronic with the dysfunction of the pain modulatory system; however, the underlying mechanisms are unclear. We found that the metabotropic glutamate receptor 5 (mGluR5) in the periaqueductal gray (PAG), the key area of endogenous pain modulation, is persistently active in normal conditions to maintain an appropriate sensory perception. In the neuropathic pain condition, Homer1a, an activity-dependent immediate early gene product, disrupted the persistent mGluR5 activity resulting in chronic pain. Remarkably a single-time blockage of the mGluR5 resulted in chronic neuropathic pain-like symptoms even in the absence of nerve injury. The decline of mGluR5 activity induced the pain modulatory dysfunction with a profound reduction of excitability of PAG neurons. These findings uncover the role of the persistent mGluR5 activity in vivo and provide new insight into how pain becomes chronic with the maladaptive coping of the PAG to pain sensation.
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Silva C, McNaughton N. Are periaqueductal gray and dorsal raphe the foundation of appetitive and aversive control? A comprehensive review. Prog Neurobiol 2019; 177:33-72. [DOI: 10.1016/j.pneurobio.2019.02.001] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2018] [Revised: 01/19/2019] [Accepted: 02/08/2019] [Indexed: 12/28/2022]
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Palazzo E, Marabese I, Luongo L, Guida F, de Novellis V, Maione S. Nociception modulation by supraspinal group III metabotropic glutamate receptors. J Neurochem 2017; 141:507-519. [DOI: 10.1111/jnc.13725] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2016] [Revised: 06/15/2016] [Accepted: 06/20/2016] [Indexed: 02/02/2023]
Affiliation(s)
- Enza Palazzo
- Department of Experimental Medicine; The Second University of Naples; Naples Italy
| | - Ida Marabese
- Department of Experimental Medicine; The Second University of Naples; Naples Italy
| | - Livio Luongo
- Department of Experimental Medicine; The Second University of Naples; Naples Italy
| | - Francesca Guida
- Department of Experimental Medicine; The Second University of Naples; Naples Italy
| | - Vito de Novellis
- Department of Experimental Medicine; The Second University of Naples; Naples Italy
| | - Sabatino Maione
- Department of Experimental Medicine; The Second University of Naples; Naples Italy
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Kolber BJ. mGluRs Head to Toe in Pain. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2015; 131:281-324. [DOI: 10.1016/bs.pmbts.2014.12.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Supraspinal basis of analgesic and clinical effects of the metabotropic glutamate mGluR1 antagonist during colonic distension in sheep. Small Rumin Res 2014. [DOI: 10.1016/j.smallrumres.2013.11.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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8
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Role of dorsolateral periaqueductal grey in the coordinated regulation of cardiovascular and respiratory function. Auton Neurosci 2013; 175:17-25. [DOI: 10.1016/j.autneu.2012.12.008] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2012] [Revised: 12/18/2012] [Accepted: 12/26/2012] [Indexed: 02/07/2023]
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Gregg LC, Jung KM, Spradley JM, Nyilas R, Suplita RL, Zimmer A, Watanabe M, Mackie K, Katona I, Piomelli D, Hohmann AG. Activation of type 5 metabotropic glutamate receptors and diacylglycerol lipase-α initiates 2-arachidonoylglycerol formation and endocannabinoid-mediated analgesia. J Neurosci 2012; 32:9457-68. [PMID: 22787031 PMCID: PMC3652685 DOI: 10.1523/jneurosci.0013-12.2012] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2011] [Revised: 05/11/2012] [Accepted: 05/17/2012] [Indexed: 11/21/2022] Open
Abstract
Acute stress reduces pain sensitivity by engaging an endocannabinoid signaling circuit in the midbrain. The neural mechanisms governing this process and molecular identity of the endocannabinoid substance(s) involved are unknown. We combined behavior, pharmacology, immunohistochemistry, RNA interference, quantitative RT-PCR, enzyme assays, and lipidomic analyses of endocannabinoid content to uncover the role of the endocannabinoid 2-arachidonoyl-sn-glycerol (2-AG) in controlling pain sensitivity in vivo. Here, we show that footshock stress produces antinociception in rats by activating type 5 metabotropic glutamate receptors (mGlu(5)) in the dorsolateral periaqueductal gray (dlPAG) and mobilizing 2-AG. Stimulation of mGlu(5) in the dlPAG with DHPG [(S)-3,5-dihydroxyphenylglycine] triggered 2-AG formation and enhanced stress-dependent antinociception through a mechanism dependent upon both postsynaptic diacylglycerol lipase (DGL) activity, which releases 2-AG, and presynaptic CB(1) cannabinoid receptors. Pharmacological blockade of DGL activity in the dlPAG with RHC80267 [1,6-bis(cyclohexyloximinocarbonylamino)hexane] and (-)-tetrahydrolipstatin (THL), which inhibit activity of DGL-α and DGL-β isoforms, suppressed stress-induced antinociception. Inhibition of DGL activity in the dlPAG with THL selectively decreased accumulation of 2-AG without altering levels of anandamide. The putative 2-AG-synthesizing enzyme DGL-α colocalized with mGlu(5) at postsynaptic sites of the dlPAG, whereas CB(1) was confined to presynaptic terminals, consistent with a role for 2-AG as a retrograde signaling messenger. Finally, virally mediated silencing of DGL-α, but not DGL-β, transcription in the dlPAG mimicked effects of DGL inhibition in suppressing both endocannabinoid-mediated stress antinociception and 2-AG formation. The results indicate that activation of the postsynaptic mGlu(5)-DGL-α cascade triggers retrograde 2-AG signaling in vivo. This pathway is required for endocannabinoid-mediated stress-induced analgesia.
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Affiliation(s)
- Laura C. Gregg
- Neuroscience Program, Biomedical and Health Sciences Institute, and
| | - Kwang-Mook Jung
- Department of Pharmacology, University of California, Irvine, Irvine, California 92697
| | | | - Rita Nyilas
- Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary
| | - Richard L. Suplita
- Psychology Department, University of Georgia, Athens, Georgia 30602-3013
| | - Andreas Zimmer
- Insitute of Molecular Psychiatry, University of Bonn, 53105 Bonn, Germany
| | - Masahiko Watanabe
- Department of Anatomy, Hokkaido University School of Medicine, Sapporo 060-8638, Japan
| | - Ken Mackie
- Department of Psychological and Brain Sciences, Indiana University, Bloomington, Indiana 47405-2204, and
| | - István Katona
- Institute of Experimental Medicine, Hungarian Academy of Sciences, H-1083 Budapest, Hungary
| | - Daniele Piomelli
- Department of Pharmacology, University of California, Irvine, Irvine, California 92697
- Unit of Drug Discovery and Development, Italian Institute of Technology, 16163 Genoa, Italy
| | - Andrea G. Hohmann
- Neuroscience Program, Biomedical and Health Sciences Institute, and
- Psychology Department, University of Georgia, Athens, Georgia 30602-3013
- Department of Psychological and Brain Sciences, Indiana University, Bloomington, Indiana 47405-2204, and
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Wilson-Poe AR, Mitchell VA, Vaughan CW. Postsynaptic mGluR mediated excitation of neurons in midbrain periaqueductal grey. Neuropharmacology 2012; 66:348-54. [PMID: 22771462 DOI: 10.1016/j.neuropharm.2012.06.057] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Revised: 06/25/2012] [Accepted: 06/26/2012] [Indexed: 11/30/2022]
Abstract
Metabotropic glutamate (mGlu) receptors modulate pain from within the midbrain periaqueductal grey (PAG). In the present study, the postsynaptic mGlu receptor mediated effects on rat PAG neurons were examined using whole-cell patch-clamp recordings in brain slices. The selective group I agonist DHPG (10 μM) produced an inward current in all PAG neurons tested which was associated with a near parallel shift in the current-voltage relationship. By contrast, the group II and III mGlu receptor agonists DCG-IV (1 μM) and l-AP4 (3 μM) produced an outward current in only 10-20% of PAG neurons tested. The DHPG induced current was concentration dependent (EC(50) = 1.4 μM), was reduced by the mGlu1 antagonist CPCCOEt (100 μM), and was further reduced by CPCCOEt in combination with the mGlu5 antagonist MPEP (10 μM). The glutamate transport blocker TBOA (30 μM) also produced an inward current, however, this was largely abolished by CNQX (10 μM) plus AP5 (25 μM). Slow EPSCs were evoked following train, but not single shock stimulation, which were enhanced by TBOA (30 μM). The TBOA enhancement of slow EPSCs was abolished by MPEP plus CPCCOEt. These findings indicate that endogenously released glutamate, under conditions in which neurotransmitter spill-over is enhanced, activates group I mGlu receptors to produce excitatory currents within PAG. Thus, postsynaptic group I mGlu receptors have the potential to directly modulate the analgesic, behavioural and autonomic functions of the PAG. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.
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Affiliation(s)
- Adrianne R Wilson-Poe
- Pain Management Research Institute, Level 13, Kolling Building, Kolling Institute of Medical Research, Northern Clinical School, The University of Sydney at Royal North Shore Hospital, St Leonards, NSW, Australia
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Jung SS, Sung KW, Lee SE, Shin HK. Capsaicin prevents the hyperalgesia induced by peripheral group I mGluRs activation. Neurosci Lett 2011; 500:197-201. [PMID: 21742015 DOI: 10.1016/j.neulet.2011.06.035] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2011] [Revised: 06/20/2011] [Accepted: 06/21/2011] [Indexed: 11/16/2022]
Abstract
Group 1 metabotropic glutamate receptors (mGluRs) are expressed in peripheral and central neural tissues and involved in peripheral and central sensitization in various pain models. However, there are limited reports that activation of peripheral group I mGluRs could evoke pain. Furthermore, any behavioral evidences could not be found out, showing what kind of afferent fibers are involved in peripheral mGluRs-mediated hyperalgesia. This study was undertaken to clarify whether peripherally injected group I mGluRs agonists could induce pain-related behaviors and capsaicin-sensitive afferent fibers might be involved in the hyperalgesia. To assess pain sensitivity, mechanical threshold for paw withdrawal response (PWT) was measured and number of spontaneous flinching behavior was counted. Intraplantar injection of group I mGluR agonist, (RS)-3,5-dihydroxyphenylglycine (DHPG) and mGluR5 agonist, (RS)-2-chloro-5-hydroxyphenyglycine (CHPG) immediately induced pain-like behaviors, such as decrease of PWT and increased number of flinchings. These agonists-induced pain-like behaviors were blocked by group I mGluRs antagonist, (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) and mGluR5 antagonist, 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP). Perineural pretreatment of 1% capsaicin solution significantly reduced pain-related behaviors induced by DHPG and CHPG, proposing that capsaicin-sensitive primary afferent fibers could be responsible for the hyperalgesia induced by activation of peripheral group I mGluRs. This study presents the first behavioral evidence that peripheral group I mGluRs activation could induce spontaneous as well as mechanical hyperalgesia and capsaicin-sensitive afferent fiber could be implicated the group I mGluR mediated hyperalgesia.
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Affiliation(s)
- Soo Suk Jung
- Department of Physiology, College of Medicine, Hanyang University, Seoul 133-791, South Korea
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12
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Saransaari P, Oja SS. Mechanisms of Inhibitory Amino Acid Release in the Brain Stem Under Normal and Ischemic Conditions. Neurochem Res 2010; 35:1948-56. [DOI: 10.1007/s11064-010-0265-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/08/2010] [Indexed: 12/23/2022]
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Substance P drives endocannabinoid-mediated disinhibition in a midbrain descending analgesic pathway. J Neurosci 2009; 29:7220-9. [PMID: 19494144 DOI: 10.1523/jneurosci.4362-08.2009] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Substance P is thought to play an essential role in several forms of supraspinally mediated analgesia. The actions of substance P on synaptic transmission within descending analgesic pathways, however, are largely unknown. Here, we used whole-cell recordings from rat midbrain slices to examine the effects of substance P on GABAergic and glutamatergic transmission within the periaqueductal gray (PAG), a key component of a descending analgesic pathway that projects via the rostral ventromedial medulla (RVM) to the spinal cord dorsal horn. We found that substance P reversibly decreased the amplitude and increased the paired-pulse ratio of evoked IPSCs recorded from identified PAG-RVM projection neurons and from unidentified PAG neurons. Substance P had no effect on miniature IPSCs, implying an indirect mode of action. The effects of substance P were abolished by metabotropic glutamate type 5 and cannabinoid CB1 receptor antagonists, but unaltered by NMDA, GABA(B), mu,delta-opioid, adenosine A(1), and 5HT(1A) receptor antagonists. Consistent with a role for endogenous glutamate in this process, substance P increased the frequency of action potential-dependent spontaneous EPSCs. Moreover, the effect of substance P on evoked IPSCs was mimicked and occluded by a glutamate transport inhibitor. Finally, these effects were dependent on postsynaptic G-protein activation and diacylglycerol lipase activity, suggesting the requirement for retrograde signaling by the endocannabinoid 2-arachidonoylglycerol. Thus, substance P may facilitate descending analgesia in part by enhancing glutamate-mediated excitation and endocannabinoid-mediated disinhibition of PAG-RVM projection neurons.
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14
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Modulation of taurine release in ischemia by glutamate receptors in mouse brain stem slices. Amino Acids 2009; 38:739-46. [DOI: 10.1007/s00726-009-0278-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2008] [Accepted: 03/11/2009] [Indexed: 10/21/2022]
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Abstract
Glutamate and gamma-amino butyric acid (GABA) are respectively two major excitatory and inhibitory neurotransmitters of the adult mammalian central nervous system. These neurotransmitters exert their action through two types of receptors: ionotropic and metabotropic receptors. While ionotropic receptors are ligand gated ion channels involved in fast synaptic transmission, metabotropic receptors belong to the superfamily of G-protein coupled receptors (GPCRs) and are responsible for the neuromodulatory effect of glutamate and GABA. Metabotropic glutamate receptors (mGluRs) and metabotropic GABA receptors (GABA-B) are present at different levels of the pain neuraxis where they regulate nociceptive transmission and pain. The present review will focus on the role of these receptors in the modulation of pain perception.
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Mechanisms of Glycine Release in Mouse Brain Stem Slices. Neurochem Res 2008; 34:286-94. [DOI: 10.1007/s11064-008-9774-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2008] [Accepted: 06/05/2008] [Indexed: 10/21/2022]
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Glutamate spillover modulates GABAergic synaptic transmission in the rat midbrain periaqueductal grey via metabotropic glutamate receptors and endocannabinoid signaling. J Neurosci 2008; 28:808-15. [PMID: 18216189 DOI: 10.1523/jneurosci.4876-07.2008] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Glutamate spillover regulates GABAergic synaptic transmission at several CNS synapses via presynaptic ionotropic and metabotropic glutamate receptors (mGluRs). We have previously demonstrated that activation of group I-III mGluRs inhibits GABAergic transmission in the midbrain periaqueductal gray (PAG), a region involved in organizing behavioral responses to threat, stress, and pain. Here, we examined the role of glutamate spillover in the modulation of GABAergic transmission in the PAG. Using whole-cell recordings from rat PAG slices, we found that evoked IPSCs were reduced by the nonspecific glutamate transport blockers DL-threo-beta-benzyloxyaspartic acid (TBOA) and L-trans-pyrrolidine-2,4-dicarboxylic acid, but not by the glial GLT1-specific blocker dihydrokainate. In contrast, TBOA had no effect on evoked IPSCs when glutamate uptake into the postsynaptic neuron was selectively impaired. TBOA increased the paired-pulse ratio of evoked IPSCs and reduced the rate but not the amplitude of spontaneous miniature IPSCs. The effect of TBOA on evoked IPSCs was abolished by the broad-spectrum mGluR antagonist (2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid (100 microM), reduced by the mGluR5-specific antagonist 2-methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP) and mimicked by the mGluR1/5 agonist (RS)-3,5-dihydroxyphenylglycine (DHPG). Furthermore, the effects of both TBOA and DHPG were reduced by the cannabinoid CB1 receptor antagonist 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (AM251). Finally, although MPEP and AM251 had no effect on single evoked IPSCs, they increased evoked IPSCs during repetitive stimulation. These results indicate that neuronal glutamate transporters limit mGluR5 activation and endocannabinoid signaling, but may be overwhelmed during conditions of elevated glutamate release. Thus, neuronal glutamate transporters play a key role in regulating endocannabinoid-mediated cross talk between glutamatergic and GABAergic synapses within the PAG.
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Lima VCF, Molchanov ML, Aguiar DC, Campos AC, Guimarães FS. Modulation of defensive responses and anxiety-like behaviors by group I metabotropic glutamate receptors located in the dorsolateral periaqueductal gray. Prog Neuropsychopharmacol Biol Psychiatry 2008; 32:178-85. [PMID: 17804134 DOI: 10.1016/j.pnpbp.2007.08.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/12/2007] [Revised: 08/01/2007] [Accepted: 08/08/2007] [Indexed: 10/22/2022]
Abstract
Glutamatergic neurotransmission in the dorsolateral periaqueductal gray (dlPAG) is related to defensive responses. However, the role of group I glutamate metabotropic receptors (mGluR) in these responses has been poorly investigated. The objective of the present study, therefore, was to test the hypothesis that interference with group I mGluR-mediated neurotransmission in dlPAG could modulate defensive responses. Male Wistar rats with cannulae aimed at the dlPAG were submitted to the following experiments: 1. intra dlPAG injections of vehicle (veh, 0.2 microL) or (RS)1-aminoindan-1,5-dicarboxylic acid (AIDA, 30-100 nmol, an mGluR1 receptor competitive antagonist) followed, 5 min later, by veh or trans-(+)-1-amino-1,3-ciclopentanedicarboxylic acid (tACPD, a group I and II mGluR agonist, 30 nmol); 2. intra-dlPAG injections of veh, AIDA (30 nmol) or 2-methyl-6-(phenylethynyl)-pyridine (MPEP, an mGluR5 receptor non-competitive antagonist, 50 nmol) followed by trans-azetidine-2,4-dicarboxylic acid (tADA, a group I mGluR agonist, 10 nmol); 3. and 4. intra-dlPAG injections of vehicle, AIDA (10-30 nmol) or MPEP (10-50 nmol) before the elevated plus maze (EPM) test; 5. intra-dlPAG injections of vehicle, AIDA (30 nmol) or MPEP (50 nmol) before the Vogel punished licking test. tACPD induced defensive responses characterized by jumps and an increased number of crossings in the observation box. These responses were attenuated by AIDA (30 nmol). tADA produced similar responses, although of lower intensity. tADA effects were prevented by AIDA and MPEP. Both drugs also produced anxiolytic-like effects in the EPM and Vogel tests when injected alone. The results suggest that group I metabotropic glutamate receptors in the dlPAG facilitate defensive responses and may also be involved in regulating anxiety-like behavior.
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Affiliation(s)
- Vivian C F Lima
- Department of Pharmacology, School of Medicine of Ribeirão Preto Campus, USP, 14049-900, Ribeirão Preto, SP, Brazil
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Abstract
Pain is an important survival and protection mechanism for animals. However, chronic/persistent pain may be differentiated from normal physiological pain in that it confers no obvious advantage. An accumulating body of pharmacological, electrophysiological, and behavioral evidence is emerging in support of the notion that glutamate receptors play a crucial role in pain pathways and that modulation of glutamate receptors may have potential for therapeutic utility in several categories of persistent pain, including neuropathic pain resulting from injury and/or disease of central (e.g., spinal cord injury) or peripheral nerves (e.g., diabetic neuropathy, radiculopathy) and inflammatory or joint-related pain (e.g., rheumatoid arthritis, osteoarthritis). This review focuses on the role of glutamate receptors, including both ionotropic (AMPA, NMDA and kainate) and metabotropic (mGlu1-8) receptors in persistent pain states with particular emphasis on their expression patterns in nociceptive pathways and their potential as targets for pharmacological intervention strategies.
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Affiliation(s)
- David Bleakman
- Neuroscience Division, Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, IN 46285, USA.
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Saransaari P, Oja SS. Characteristics of taurine release in slices from adult and developing mouse brain stem. Amino Acids 2006; 31:35-43. [PMID: 16680399 DOI: 10.1007/s00726-006-0290-5] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2005] [Accepted: 01/17/2006] [Indexed: 10/24/2022]
Abstract
Taurine has been thought to function as a regulator of neuronal activity, neuromodulator and osmoregulator. Moreover, it is essential for the development and survival of neural cells and protects them under cell-damaging conditions. Taurine is also involved in many vital functions regulated by the brain stem, including cardiovascular control and arterial blood pressure. The release of taurine has been studied both in vivo and in vitro in higher brain areas, whereas the mechanisms of release have not been systematically characterized in the brain stem. The properties of release of preloaded [(3)H]taurine were now characterized in slices prepared from the mouse brain stem from developing (7-day-old) and young adult (3-month-old) mice, using a superfusion system. In general, taurine release was found to be similar to that in other brain areas, consisting of both Ca(2+)-dependent and Ca(2+)-independent components. Moreover, the release was mediated by Na(+)-, Cl(-)-dependent transporters operating outwards, as both Na(+)-free and Cl(-) -free conditions greatly enhanced it. Cl(-) channel antagonists and a Cl(-) transport inhibitor reduced the release at both ages, indicating that a part of the release occurs through ion channels. Protein kinases appeared not to be involved in taurine release in the brain stem, since substances affecting the activity of protein kinase C or tyrosine kinase had no significant effects. The release was modulated by cAMP second messenger systems and phospholipases at both ages. Furthermore, the metabotropic glutamate receptor agonists likewise suppressed the K(+)-stimulated release at both ages. In the immature brain stem, the ionotropic glutamate receptor agonists N-methyl-D-aspartate (NMDA) and 2-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) potentiated taurine release in a receptor-mediated manner. This could constitute an important mechanism against excitotoxicity, protecting the brain stem under cell-damaging conditions.
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Affiliation(s)
- P Saransaari
- Tampere Brain Research Center, Medical School, University of Tampere, Tampere, Finland.
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21
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Saransaari P, Oja SS. Characteristics of GABA release in mouse brain stem slices under normal and ischemic conditions. Neurochem Res 2006; 30:1549-56. [PMID: 16362774 DOI: 10.1007/s11064-005-8833-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/23/2005] [Indexed: 12/21/2022]
Abstract
GABA is known to be the inhibitory neurotransmitter in the majority of brain stem nuclei. The release of GABA has been extensively studied both in vivo and in vitro in higher brain areas, whereas the mechanisms of release in the brain stem have not been systemically characterized. The properties of preloaded [3H]GABA were now investigated in mouse brain stem slices, using a superfusion system. The basal release was enhanced by K+ stimulation (50 mM K+) and under various cell-damaging conditions (ischemia, hypoglycemia, the presence of free radicals and metabolic poisons). No K+-stimulated release was discernible in the absence of Ca2+, indicating that the release was at least partly Ca2+-dependent. Moreover, the release was increased when Na+ or Cl- was omitted from the superfusion medium. GABA and beta-alanine stimulated the release, confirming the involvement of the reversed function of GABA transporters. Incubation of the slices with the anion channel inhibitors diisothiocyanostilbene and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonate and with the Cl- uptake inhibitor 9-anthracenecarboxylic acid also reduced GABA release, demonstrating that a part of it comprises leakage through anion channels. All these mechanisms were involved in the ischemia-induced GABA release, which was over 4-fold greater than the release in normoxia. Contrary to the other brain areas, GABA release in the brain stem was not affected by ionotropic glutamate receptors but may be modulated by metabotropic receptors. This ischemia-induced GABA release might constitute an important mechanism against excitotoxicity, protecting the brain stem under cell-damaging conditions.
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Affiliation(s)
- Pirjo Saransaari
- Tampere Brain Research Center, Medical School, University of Tampere, and Tampere University Hospital, Finland.
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Drew GM, Vaughan CW. Multiple metabotropic glutamate receptor subtypes modulate GABAergic neurotransmission in rat periaqueductal grey neurons in vitro. Neuropharmacology 2004; 46:927-34. [PMID: 15081789 DOI: 10.1016/j.neuropharm.2004.01.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2003] [Revised: 12/08/2003] [Accepted: 01/19/2004] [Indexed: 10/26/2022]
Abstract
The effect of metabotropic glutamate receptor (mGluR) activation on GABAergic synaptic transmission in rat periaqueductal grey (PAG) neurons was examined using whole-cell patch-clamp recordings in brain slices. The selective groups I, II and III mGluR agonists DHPG (10-30 microM), DCG-IV (1-3 microM) and L-AP4 (10-30 microM) inhibited electrically evoked GABA(A) mediated inhibitory postsynaptic currents (IPSCs) in all PAG neurons tested. DCG-IV and L-AP4 also reduced the frequency of spontaneous IPSCs, while DHPG produced both increases and decreases in spontaneous IPSC frequency in a dose dependent manner. In the presence of TTX, DHPG, DCG-IV and L-AP4 all reduced the frequency of spontaneous miniature IPSCs, but had no effect on their amplitudes. The DHPG, DCG-IV and L-AP4 effects on miniature IPSCs were dose dependent (EC(50)s=1.4, 0.055 and 0.52 microM, respectively) and were reduced by the selective mGluR antagonists MCPG, EGLU and MSOP, respectively. These results indicate that GABAergic synaptic transmission within the PAG is reduced by groups I, II and III mGluR activation via a presynaptic mechanism and is increased by group I mGluR activation via an action potential dependent mechanism. The finding of convergent groups I, II and III mGluR-mediated inhibition of synaptic transmission is novel and indicates that all groups of mGluRs have the potential to modulate the constellation of analgesic, behavioural and autonomic functions within the PAG.
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Affiliation(s)
- Geoffrey M Drew
- Pain Management Research Institute, Northern Clinical School, Royal North Shore Hospital, E25, University of Sydney, Sydney, NSW 2006, Australia.
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de Novellis V, Marabese I, Palazzo E, Rossi F, Berrino L, Rodella L, Bianchi R, Rossi F, Maione S. Group I metabotropic glutamate receptors modulate glutamate and gamma-aminobutyric acid release in the periaqueductal grey of rats. Eur J Pharmacol 2003; 462:73-81. [PMID: 12591098 DOI: 10.1016/s0014-2999(03)01342-6] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In this study, we investigated the effects of group I metabotropic glutamate (mglu) receptor ligands on glutamate and gamma-aminobutyric acid (GABA) extracellular concentrations at the periaqueductal grey level by using in vivo microdialysis. An agonist of group I mglu receptors, (S)-3,5-dihydroxyphenylglycine [(S)-3,5-DHPG, 1 and 2 mM], as well as a selective agonist of mglu(5) receptors, (RS)-2-chloro-5-hydroxyphenylglycine (CHPG, 2 and 4 mM), both increased dialysate glutamate and GABA concentrations. 7-(Hydroxyimino)cyclopropa-[b]-chromen-1alpha-carboxylate ethyl ester (CPCCOEt, 1 mM), a selective mglu(1) receptor antagonist, and 2-methyl-6-(phenylethynyl)pyridine (MPEP, 0.5 mM), a selective mglu(5) receptor antagonist, perfused in combination with DHPG, antagonized the effect induced by DHPG on the extracellular glutamate and GABA concentrations. MPEP (0.5 mM), perfused in combination with CHPG, antagonized the increased glutamate and GABA extracellular levels induced by CHPG. MPEP (1 mM) decreased the extracellular concentrations of glutamate but did not modify the dialysate GABA concentrations. Moreover, as the intra-periaqueductal grey perfusion of (RS)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid [(RS)-CPP, 100 microM], a selective N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, did not change the extracellular concentrations of glutamate, this suggests that the MPEP-induced decrease in glutamate is not a consequence of NMDA receptor blockade. These data show that group I mglu receptors in the periaqueductal grey may modulate the release of glutamate and GABA in awake, freely moving rats. In particular, mglu(5), but not mglu(1), receptors seem to be functionally active on glutamate terminals.
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Affiliation(s)
- Vito de Novellis
- Department of Experimental Medicine, Section of Pharmacology L. Donatelli, Faculty of Medicine and Surgery, Second University of Naples, Via Costantinopoli, 16 80138 Naples, Italy.
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de Novellis V, Marabese I, Uliano R, Palazzo E, Scafuro A, sca Rossi F, Maione S. Type I and II metabotropic glutamate receptors modulate periaqueductal grey glycine release: interaction between mGlu2/3 and A1 adenosine receptors. Neuropharmacology 2002; 43:1061-9. [PMID: 12504911 DOI: 10.1016/s0028-3908(02)00227-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In this study we investigated the effects of type I and II mGlu receptors ligands in glycine extracellular concentrations at the periaqueductal gray (PAG) level by using in vivo microdialysis, in conscious rats. An agonist of type I mGlu receptors, (S)-3,5-DHPG (1 and 5 mM), but not a selective agonist for mGlu5 receptors, CHPG (3 and 5 mM), was noticed to increase the dialysate glycine levels in a concentration-dependent manner (60+/-15% and 136+/-13%, respectively). CPCCOEt (1mM), a selective mGlu1 receptor antagonist, perfused in combination with (S)-3,5-DHPG, counteracted the effect induced by (S)-3,5-DHPG, but did not change per se the extracellular PAG glycine values, even at the highest dosage used (2 mM). MPEP (1 and 2 mM), a selective antagonist of mGlu5 receptor, did not modify extracellular glycine level. An agonist of type II mGlu receptors, 2R,4R-APDC (25 and 50 microM), decreased the dialysate glycine in a concentration-dependent manner (-26+/-4% and -54+/-6%, respectively). The 2R,4R-APDC-induced decrease in extracellular glycine was prevented by EGlu (0.5 mM), a selective type II mGlu receptors antagonist. EGlu (0.5 and 1 mM), per se, led to a significant decrease (-56+/-7% and -57+/-2%, respectively) in extracellular PAG glycine too. This effect was prevented by DPCPX (100 microM), a selective antagonist for A1 adenosine receptors, but was not affected by CPA (1 mM), a selective A1 adenosine receptors agonist. Intra-PAG perfusion of CPA (0.1-1 mM) decreased the extracellular PAG glycine values (-47+/-13%) with 1 mM concentration. The CPA-induced effect was prevented by DPCPX (100 microM), and resulted to be additive with the 2R,4R-APDC-induced decrease in glycine values. DPCPX (1 mM) increased per se extracellular glycine (48+/-7%) at the highest dose used. Dipyridamole (100 microM), an inhibitor of both adenosine reuptake and phosphodiesterases, decreased extracellular glycine (-28+/-7%). Extracellular concentrations of glutamine never changed throughout this study. These data show opposing effects of type I and II mGlu receptors in the regulation of PAG glycine values. Moreover, functional interaction between type II mGlu and adenosine A1 receptors, which possibly operate through a common transductional pathway, may be relevant in the physiological control of glycine release in awake, freely moving rats at the periaqueductal gray matter.
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Affiliation(s)
- V de Novellis
- Department of Experimental Medicine, Faculty of Medicine and Surgery, Second University of Naples, Via Costantinopoli, 16 80138, Naples, Italy
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Reuss B, Leung DS, Ohlemeyer C, Kettenmann H, Unsicker K. Regionally distinct regulation of astroglial neurotransmitter receptors by fibroblast growth factor-2. Mol Cell Neurosci 2000; 16:42-58. [PMID: 10882482 DOI: 10.1006/mcne.2000.0857] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Fibroblast growth factor (FGF)-2 is an abundant astroglial cytokine. We have previously shown that FGF-2 downregulates gap junctions in primary astroglial cultures (B. Reuss et al., 1998, Glia 22, 19-30). We demonstrate now that FGF-2 induces astroglial dopamine (DA) sensitivity and D1 dopamine-receptor (D1DR) antigen and message in cortical and striatal astroglial cultures. On the functional level 10 micromol/L DA triggered transient increases in astroglial [Ca(2+)](i). In gap-junction-coupled cells, no FGF-2-dependent changes in proportions of DA-responsive cells were observable. However, uncoupling with octanol or 18alpha-glycirrhetinic acid isolated the smaller population of astrocytes intrinsically sensitive to DA which was significantly increased by FGF-2 in cortical and striatal cultures. Administration of DR-specific substances revealed that FGF-2 upregulated D1DR. These results indicate that downregulation of astroglial gap junctions by FGF-2 is accompanied by an upregulation of D1DR and DA sensitivity, adding a new aspect to the role of FGF-2 in the regulation of brain functions.
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Affiliation(s)
- B Reuss
- Neuroanatomy, University of Heidelberg, Im Neuenheimer Feld 307, Heidelberg, D-69120, Germany
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Abstract
The highly disagreeable sensation of pain results from an extraordinarily complex and interactive series of mechanisms integrated at all levels of the neuroaxis, from the periphery, via the dorsal horn to higher cerebral structures. Pain is usually elicited by the activation of specific nociceptors ('nociceptive pain'). However, it may also result from injury to sensory fibres, or from damage to the CNS itself ('neuropathic pain'). Although acute and subchronic, nociceptive pain fulfils a warning role, chronic and/or severe nociceptive and neuropathic pain is maladaptive. Recent years have seen a progressive unravelling of the neuroanatomical circuits and cellular mechanisms underlying the induction of pain. In addition to familiar inflammatory mediators, such as prostaglandins and bradykinin, potentially-important, pronociceptive roles have been proposed for a variety of 'exotic' species, including protons, ATP, cytokines, neurotrophins (growth factors) and nitric oxide. Further, both in the periphery and in the CNS, non-neuronal glial and immunecompetent cells have been shown to play a modulatory role in the response to inflammation and injury, and in processes modifying nociception. In the dorsal horn of the spinal cord, wherein the primary processing of nociceptive information occurs, N-methyl-D-aspartate receptors are activated by glutamate released from nocisponsive afferent fibres. Their activation plays a key role in the induction of neuronal sensitization, a process underlying prolonged painful states. In addition, upon peripheral nerve injury, a reduction of inhibitory interneurone tone in the dorsal horn exacerbates sensitized states and further enhance nociception. As concerns the transfer of nociceptive information to the brain, several pathways other than the classical spinothalamic tract are of importance: for example, the postsynaptic dorsal column pathway. In discussing the roles of supraspinal structures in pain sensation, differences between its 'discriminative-sensory' and 'affective-cognitive' dimensions should be emphasized. The purpose of the present article is to provide a global account of mechanisms involved in the induction of pain. Particular attention is focused on cellular aspects and on the consequences of peripheral nerve injury. In the first part of the review, neuronal pathways for the transmission of nociceptive information from peripheral nerve terminals to the dorsal horn, and therefrom to higher centres, are outlined. This neuronal framework is then exploited for a consideration of peripheral, spinal and supraspinal mechanisms involved in the induction of pain by stimulation of peripheral nociceptors, by peripheral nerve injury and by damage to the CNS itself. Finally, a hypothesis is forwarded that neurotrophins may play an important role in central, adaptive mechanisms modulating nociception. An improved understanding of the origins of pain should facilitate the development of novel strategies for its more effective treatment.
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Affiliation(s)
- M J Millan
- Institut de Recherches Servier, Psychopharmacology Department, Paris, France
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Azkue JJ, Mateos JM, Elezgarai I, Benítez R, Lázaro E, Streit P, Grandes P. Glutamate-like immunoreactivity in ascending spinofugal afferents to the rat periaqueductal grey. Brain Res 1998; 790:74-81. [PMID: 9593831 DOI: 10.1016/s0006-8993(98)00050-x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The midbrain periaqueductal gray is a key structure for the mediation of an integrated defence behaviour. Although a prominent role for glutamate in PAG mechanisms is supported by both behavioural and morphological studies, whether PAG afferents conveying somatosensory information constitute a source of glutamatergic input to the PAG remains unknown. Here, we have compared the projection pattern of orthogradely-labelled spinoannular fibres with the distribution of glutamate-like immunoreactivity in the PAG at the light microscopic level. Transaxonal labelling was observed throughout the whole rostrocaudal axis of the PAG except for the dorsolateral regions. Cell-processes and terminal-reminiscent puncta were strongly immunoreactive in all PAG regions, including the dorsolateral areas. To ascertain whether glutamate-immunoreactive puncta observed at light microscopy indeed constituted axon terminals of the spinoannular system, glutamate-like immunoreactivity was assessed in orthogradely-labelled synaptic terminals using a post-embedding immunogold procedure for electron microscopy. Quantitative analysis of gold particle densities revealed over twice as strong an immunoreactivity in anatomically-identified spinoannular axon terminals as in dendrites postsynaptic to them, perikarya and inhibitory Gray II synapses, as well as an over 5-fold heavier immunolabelling than in glial profiles. These findings reveal that glutamate is accumulated in synaptic terminals of the spinoannular system, supporting a neurotransmitter role for this acidic amino acid in spinofugal afferents to the PAG.
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Affiliation(s)
- J J Azkue
- Department of Neurosciences, School of Medicine and Dentistry, University of the Basque Country, PO Box 699, E-48080 Bilbao, Spain.
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